> This seemed pretty straight-forward so I thought I'd take a shot at
> implementing this as my first attempt at kernel hacking.
We all had to start somewhere ... :)
> However, I've
> run into a problem in the user space end of it. In
> /usr/include/asm/types.h, dev_t is defined as 'short'. In
> /usr/include/bits/types.h dev_t is defined as a '_u_quad_t', so the
> usbdevfs_driver_devinfo structure has different sizes in user and kernel
> space. What's the right thing to do?
sixteen bit dev_t ... though I'm puzzled why "_u_quad_t" would
appear anywhere!
> Also, the USB printer module doesn't save its major device number. Is
> just using the value in major.h (USB_CHAR_MAJOR) correct?
I'd use USB_MAJOR from <linux/usb.h>, like printer.c does when
it does the devfs_register() call.
- Dave
>
> Thanks,
> Allen
>
> David Brownell wrote:
> >
> > > Would it be possible (or reasonable) to add an ioctl to usbdevfs which
> > > can ask for this information via the /proc/bus/usb/###/### interface? Or
> > > should the printer.o module execute a user-space helper app to do this
> > > configuration itself?
> >
> > IMHO, either of those would be reasonable 2.4 solutions. I'd likely
> > want to see the ioctl, since scenarios have wanted this feature before.
> > But that wouldn't work with non-USB printers; "printer hotplug" should
> > IMHO happen at some point, too.
> >
> > That is, perhaps adding something like this to <linux/usbdevice_fs.h>
> >
> > struct usbdevfs_driver_devinfo {
> > int type; /* S_IFCHR or S_IFBLK from <sys/stat.h> */
> > dev_t dev; /* major/minor */
> > }
> > #define USBDEVFS_DRIVER_DEVINFO \
> > _IOR('U',22, struct usbdevfs_driver_devinfo)
> >
> > and the driver (printer.c) would get updated
> >
> > static int printer_ioctl (
> > struct usb_device *dev,
> > unsigned int ioctl_code,
> > void *user_data
> > ) {
> > switch (ioctl_code) {
> > case USBDEVFS_DRIVER_DEVINFO:
> > ... user_data is a struct usbdevfs_driver_devinfo
> > ... fill it out and return
> > default:
> > return -ENOSYS;
> > }
> > }
> >
> > static struct usb_driver
> > ...
> > ioctl: printer_ioctl;
> > }
> >
> > Then userspace would call it using the USBDEVFS_IOCTL mechanism.
> > Printer would be the first to start reporting useful info with it.
> >
> > - Dave
>
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